This invention relates to display and use of terrain elevation data to evaluate radar product data and is particularly applicable to fields of application where information regarding actual radar coverage is required.
Significant problems exist in the presentation, display, and interpretation of radar data that result for artifacts present in the data that are unrelated to the primary observation objective of the radar. For example, the United States Government operates a network of WSR-88D weather surveillance radars in the continental US, Alaska and Hawaii which provide real-time weather information. The data from these radars is adversely affected (as is data from other radars) by many factors. These factors include at least: terrain features, refraction of the radar beam in the atmosphere, the presence of non-meteorological scatters in the atmosphere (e.g. birds, insects, dust, ash, chaff, etc.), RF interference, signal processing protocols, solar interference, etc. Various algorithmic processes have been produced to ameliorate the effects of these factors on the radar data and radar data image displays, and in applications which utilize the radar data, with varying levels of success. For many of these processes, having an improved understanding of the radar field itself is believed to be advantageous. Accordingly, by producing radar coverage, radar blockage, and clutter region maps which can be used by these various algorithmic processes, better image data can be had, and the radar data made more useful and reliable.
The primary effects of terrain on radar data quality are unique in that they are relatively deterministic because terrain doesn""t move. Therefore, we decided to evaluate how terrain elevation data can be used to assess the quality of the data generated by the WSR-88D radars.
Many of the WSR-88D radars are sited at locations where terrain features extend into the volume of the atmosphere being scanned by the radar for some portion of the lower elevation tilts. There are two primary effects of these terrain features. The most significant effect is that the ability of the radar to xe2x80x9cseexe2x80x9d the atmosphere behind terrain obstructions is impaired. The second effect (which is generally not as significant) is the presence of persistent ground clutter returns that contaminate the radar product data at the locations where terrain features extend into the path of the radar beam. Accordingly this invention developed and employed techniques for generating terrain-based radar coverage, radar blockage, and clutter region maps to identify regions of the radar product data that may be degraded due to the effects of terrain. The detailed description below describes the models used for generating these maps, and summarizes the results of our evaluation of the correlation between these maps and radar product data. The evaluation of the accuracy of the terrain-based radar coverage and clutter region maps indicates that they can be effectively utilized to assess the accuracy of radar product data. The detailed description of the invention and the examples provided are based on WSR-88D radar data.
The primary use of these maps is to allow for the development of improved displays for presenting and interpreting radar product data, and for development of improved algorithms that utilize these terrain-based radar coverage, blockage, and clutter region maps for more accurate processing of radar product data.
The algorithm descriptions and examples presented in this invention are based on the terrain elevation data obtained from the Digital Elevation Model (DEM) terrain elevation data base. The DEM data is derived from the National Imagery and Mapping Agency (NIMA) Digital Terrain Elevation Data (DTED) Level 1 data base. The DEM data is provided in a uniform matrix with a horizontal grid point spacing of 3 arc seconds (nominally 90 meters) and a terrain elevation resolution of one meter.
It should be recognized that the teachings of this invention can apply to other types of radars, and to other sources and resolutions of terrain elevation data, and can be extended to include other sources of elevation information of similar quality, particularly for example so-called xe2x80x9cculturalxe2x80x9d data bases which contain information on location and elevation of man-made structures within a radar coverage area.
By recognizing that if we generate a radar-centered maximum terrain elevation data array for a radar coverage area that we can substantially improve the qualification of radar data from such a coverage area, several applications for this qualified data become apparent. But to do so we also need to use this data to produce radar coverage, blockage, and/or clutter maps for single tilt radar products, at least. It is also and perhaps more usefully available to produce elevation layer radar products from this data as well. Further application can be had to generate radar product clutter region maps as well as radar coverage maps for radar mosaic products.
Accordingly, described herein are preferred embodiment algorithmic processes for producing such maps and illustrations of how these become useful in producing data products and radar display images, qualified by the blockage, coverage and/or clutter data produced as a result of use of the processes taught in this patent.